A Guide To Preventative Offloading Of Diabetic Foot Ulcers
Increased plantar pressure levels occur in patients with structural abnormalities such as Charcot’s neuropathy, clawtoes, hammertoes or other foot deformities. These irregularities can cause disruptions in the shape of the foot. Motor neuropathy is frequently associated with diabetic neuropathy. This in turn can lead to elevated foot pressures and ulceration.7 The combination of a deformed foot, loss of sensation, motor neuropathy and inadequate offloading may lead to tissue damage, ulceration, infection, amputations and death. Even in a patient with adequate perfusion, once an ulcer forms, studies indicate that healing is still delayed unless one catches the ulcer early and offloads it.4 Once an ulcer has healed, the rate of recurrence is 40 percent over four months.8
Furthermore, individuals with diabetes have a 30-fold higher lifetime risk of undergoing an amputation in the lower extremity in comparison to non-diabetics. Those with diabetes have at least a 10-fold greater risk of being hospitalized for bone and soft tissue infections in the lower extremity than non-diabetics.9 Infected foot wounds comprise about two-thirds of lower extremity amputations. Infection is exceeded only by gangrene as an indication for diabetic amputations of the lower extremity.9
There are many new possible solutions that one may use in conjunction with offloading modalities. These modalities include living skin substitutes, stem cells and topically applied growth factors. The key component with all of these treatment options is that the mechanical environment must be controlled so as not to destroy the modality. Decreasing pressure and strain rate are important factors for offloading.8 Pressure is the exertion of force upon a surface by an object in contact with it. This is measured as force per unit of area (P = F/A). Strain rate (ε.) is the rate of change in force with respect to time (dε/dt).
Many patients with diabetic foot ulcers are obese. Patients suffering with diabetic foot ulcers place 2 to 2.5 times their body weight on the wound, thereby increasing pressure and strain with each step.7 The easiest way to decrease strain rate is to decelerate the speed at which the foot hits the ground as well as shortening the time the foot is in contact with the ground. Nonetheless, most patients with diabetic foot ulcers suffer from neuropathy and are unable to decelerate as they step on the ground. Therefore, they tend to step more forcefully in comparison to those without neuropathy. Effective offloading modalities address both force and strain rate.7
A Closer Look At The Potential Of Offloading Devices
Total contact casts. Several studies support the total contact cast (TCC) as the gold standard offloading device for diabetic foot ulcers. Researchers have shown that offloading methods such as custom insoles, shoes or pads heal fewer wounds in comparison to the total contact cast. In a 2000 study, Hanft and Surprenant found that the percentage of DFU closures after five weeks was 88 percent from TCC, 63 percent from 3-D walkers and custom insoles, and 55 percent from custom sandals with three layers of foam.10
However, some clinicians may argue that the meticulous detail and time required to prepare and apply a TCC is incompatible with their methodology of practice. Patients who are unable to readily identify pressure points within a TCC, frail individuals with motor difficulties or morbidly obese patients are not ideal candidates for this device.11
Alternatives to the TCC include: the Charcot restraint orthotic walker (CROW), a controlled ankle motion (CAM) walker, ankle foot orthoses (AFO) and wedge shoes.